1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method and a computer readable medium.
2. Description of Related Art
The spread of cloud computing has enabled arbitrary output of images uploaded in clouds by output apparatuses connected to the respective clouds.
In an environment in which such cloud can be used, the output characteristic of an output apparatus to output an image is not certain when the image is generated. Since it is not possible to generate an image corresponding to the output characteristic of the output apparatus, there have been cases where the image cannot be reproduced sufficiently and the output image has unintended image quality depending on the output characteristic.
Especially, image information is lost when images are generated by converting color images into monochrome images and further performing binarization. Thus, the images have a tendency to have unintended image quality when the images are output.
For example, when a color image of three colors R (red), G (green) and B (blue) is converted into a monochrome image, a grayscale monochrome image is generated by using only the image of green color in order to perform the processing rapidly in some cases. In this case, since two color images among the three color images are discarded, the image information is reduced to one-third. Furthermore, since binarization is performed to convert the image having the data amount of 8 bit for one pixel, for example, into an image of 1 bit, the image information is further reduced to one-eighth.
Also in a case of generating an image in JPEG format, since the JPEG format is lossy compression and generates the loss of image information, the output image is likely to have unintended image quality.
In addition, since the image in JPEG format is generated via discrete cosine transform (DCT) by the block unit of 8×8 pixels, a regular pattern of isolated pixels is likely to be generated by the block unit of 8×8 pixels. Depending on the output characteristic of the output apparatus, there have been cases where the isolated pixels cannot be reproduced sufficiently and the output image has low reproducibility for low gradation portions.
Generally, in order to improve gradation properties of images, the images are output by performing tone correction (see Japanese Patent Application Laid Open Publication No. H10-13685 for example), image processing according to the type of halftone image (see Japanese Patent Application Laid Open Publication No. H9-51438, for example), and such like.
However, an object of general tone correction is to correct gradation so that the gradation characteristic of the output image match the intended gradation characteristic, and thus, the change of image pattern itself is not intended. Since the image pattern after tone correction is not necessarily a pattern reproducible by the output apparatus, the user cannot necessarily reproduce the image with intended image quality.